Write a summer and discussion chap-5,6,7 and 8One example of that down here:Chapter 5, the book explains membrane structure and g

Because learning changes everything.®

Chapter 5

Lecture Outline

See separate PowerPoint slides for all

figures and tables pre-inserted into

PowerPoint without notes and animations.

© 2020 McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.

No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.

© McGraw-Hill Education 2

Chapter 5

Membrane Structure, Synthesis and Transport

Key Concepts:

• Membrane Structure

• Fluidity of Membranes

• Synthesis of Membrane Components in Eukaryotic Cells

• Overview of Membrane Transport

• Transport Proteins

• Exocytosis and Endocytosis

© McGraw-Hill Education 3

Membrane Structure

• The framework of the membrane is the phospholipid bilayer

• Phospholipids are amphipathic molecules Hydrophobic (water-fearing) region faces in

Hydrophilic (water-loving) region faces out

• Membranes also contain proteins and carbohydrates

• The two leaflets (halves of bilayer) are asymmetrical, with different amounts of each component

© McGraw-Hill Education 4

Fluid-mosaic model

• Membrane is considered a mosaic of lipid, protein, and carbohydrate molecules

• Membrane resembles a fluid because lipids and proteins can move relative to each other within the membrane

© McGraw-Hill Education 5

Figure 5.1

© McGraw-Hill Education 6

Proteins bound to membranes

Integral or intrinsic membrane proteins

Transmembrane proteins

• Region(s) are physically embedded in the hydrophobic portion of the phospholipid bilayer

Lipid-anchored proteins

• An amino acid of the protein is covalently attached to a lipid

Peripheral or extrinsic membrane proteins

Noncovalently bound either to integral membrane proteins that project out from the membrane, or to polar head groups of phospholipids

© McGraw-Hill Education 7

Figure 5.2

© McGraw-Hill Education 8

Approximately 20 to 30% of All Genes Encode Transmembrane Proteins

• Membranes are important medically as well as biologically

• Computer programs can be used to predict the number of transmembrane proteins

• Estimated percentage of membrane proteins is substantial: 20 to 30% of all genes may encode transmembrane proteins

• This trend is found throughout all domains of life including archaea, bacteria, and eukaryotes

• Function of many genes is unknown – study may provide better understanding and better treatments for disease

© McGraw-Hill Education 9

Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.

Table 5.2

Table 5.2 Estimated Percentage of Genes That Encode Transmembrane Proteins*

Organism Percentage of protein-encoding genes that encode transmembrane proteins

Archaea

Archaeoglobus fulgidus 24.2

Methanococcus jannaschii 20.4

Pyrococcus horikoshii 29.9

Bacteria

Escherichia coli 29.9

Bacillus subtilis 29.2

Haemophilus influenzae 25.3

Eukaryotes

Homo sapiens 29.7

Drosophila melanogaster 24.9

Arabidopsis thaliana 30.5

Saccharomyces cerevisiae 28.2

* Source: Stevens, A. J., and Arkin, T. I. 2000. Do More Complex Organisms Have a Greater Proportion of Membrane Proteins in Their Genomes? Proteins 39: 417 to 420.

© McGraw-Hill Education 10

Fluidity of Membranes

• Membranes are semifluid

• Most lipids can rotate freely around their long axes and move laterally within the membrane leaflet

• But “flip-flop” of lipids from one leaflet to the opposite leaflet does not occur spontaneously

• Flippase requires ATP to transport lipids between leaflets

© McGraw-Hill Education 11

Figure 5.3

a) Spontaneous lipid movements b) Lipid movement via flippase

© McGraw-Hill Education 12

Lipid rafts

• Certain lipids associate strongly with each other to form lipid rafts

• A group of lipids floats together as a unit within the larger sea of lipids in the membrane

• Composition of lipid raft is different than rest of membrane

High concentration of cholesterol

Unique set of membrane proteins

© McGraw-Hill Education 13

Factors affecting fluidity

• Length of fatty acyl tails Shorter acyl tails are less likely to interact, which makes the membrane more fluid

• Presence of double bonds Double bond creates a kink in the fatty acyl tail, making it more difficult for neighboring tails to interact and making the bilayer more fluid

• Presence of cholesterol Cholesterol tends to stabilize membranes

Effects vary depending on temperature

© McGraw-Hill Education 14

Experiments on lateral movement

• Larry Frye and Michael Edidin experiment, 1970

• Demonstrated the lateral movement of membrane proteins

• Mouse and human cells were fused

• Temperature treatment – 0 Celsius or 37 Celsius

• Mouse membrane protein H-2 fluorescently labeled

• Cells at 0 Celsius – label stays on mouse side

• Cells at 37 Celsius – label moves over entire fused cell

© McGraw-Hill Education 15

Figure 5.4

1. Add agents that cause mouse cell and human cell to fuse.

2. Lower the temperature to 0 Celsius and add a

fluorescently labeled antibody that recognizes the mouse H-2 protein in the plasma membrane. Observe with a fluorescence microscope. H-2 protein is unable to move laterally and remains on one side of the fused cell.

Incubate cell at 37 Celsius, then cool to 0 Celsius and add a fluorescently labeled antibody that recognizes the mouse H-2 protein in the plasma membrane. Observe with a fluorescence microscope. Due to lateral movement at 37 Celsius,

the mouse H-2 protein is distributed throughout the fused cell surface.

© McGraw-Hill Education 16

Not all integral membrane proteins can move

• Depending on the cell type, 10 to 70% of membrane proteins may be restricted in their movement

• Integral membrane proteins may be bound to components of the cytoskeleton, which restricts the proteins from moving laterally

• Membrane proteins may be also attached to molecules that are outside the cell, such as the interconnected network of proteins that forms the extracellular matrix

© McGraw-Hill Education 17

Figure 5.5

© McGraw-Hill Education 18

Synthesis of Membrane Components in Eukaryotic Cells

Synthesis of Lipids

• In eukaryotes, the cytosol and endomembrane system work together to synthesize lipids

• Fatty acid building blocks are made via enzymes in cytosol or taken into cells from food

• Process occurs at cytosolic leaflet of the smooth Endoplastic Reticulum (ER)

© McGraw-Hill Education 19

Figure 5.6

1. In the cytosol, fatty acids are activated by the attachment of a CoA molecule.

2. The activated fatty acids bond to glycerol-phosphate and are inserted into the cytosolic leaflet of the ER membrane via acyl transferase.

3. The phosphate is removed by a phosphatase enzyme.

4. A choline already linked to phosphate is attached via choline phosphotransferase.

5. Flippases transfer some of the phospholipids to the other leaflet.

© McGraw-Hill Education 20

Transfer of lipids to other membranes

• Lipids in ER membrane can diffuse laterally to nuclear envelope

• Transported via vesicles to Golgi, lysosomes, vacuoles, or plasma membrane

• Lipid exchange proteins – extract lipid from one membrane for insertion in another

© McGraw-Hill Education 21

Synthesis of Transmembrane Proteins

• Except for proteins destined for semiautonomous organelles, most transmembrane proteins are directed to the ER membrane first

• From the ER, membrane proteins can be transferred via vesicles to other membranes of the cell

© McGraw-Hill Education 22

Figure 5.7

1. A protein begins synthesis into the ER, and the ER signal sequence is cleaved.

2. Polypeptide synthesis continues, and a hydrophobic transmembrane segment is made as the polypeptide is being threaded through the channel.

3. Polypeptide synthesis is completed, and the transmembrane segment remains in the membrane.

© McGraw-Hill Education 23

Glycosylation 1

• Process of covalently attaching a carbohydrate to a protein or lipid Glycolipid – carbohydrate to lipid Glycoprotein – carbohydrate to protein

• Can serve as recognition signals for other cellular proteins

• Often play a role in cell surface recognition

• Helps protect proteins from damage

© McGraw-Hill Education 24

Glycosylation 2

N-linked Glycosylation

• Attachment of carbohydrate to nitrogen atom of asparagine side chain

O-linked Glycosylation

• Addition of sugars to oxygen atom of serine or threonine side chains

• Occurs only in Golgi

© McGraw-Hill Education 25

Figure 5.8

1. Prior to glycosylation of a polypeptide, a group of 14 sugars is built onto a lipid in the ER membrane.

2. Oligosaccharide transferase removes the carbohydrate tree from the lipid and transfers it to an asparagine in the polypeptide.

3. Polypeptide synthesis is completed.

© McGraw-Hill Education 26

Membrane Transport

• The plasma membrane is selectively permeable

• Allows the passage of some ions and molecules but not others

• This structure ensures that: Essential molecules enter

Metabolic intermediates remain

Waste products exit

© McGraw-Hill Education 27

Ways to move across membranes

Passive transport Requires no input of energy – down or with gradient

Passive diffusion – Diffusion of a solute through a membrane without transport protein

Facilitated diffusion – Diffusion of a solute through a membrane with the aid of a transport protein

Active transport Requires energy – up or against gradient

© McGraw-Hill Education 28

Figure 5.9

a) Simple diffusion—passive transport b) Facilitated diffusion — passive transport c) Active transport

Simple diffusion across a membrane is the movement of a solute down a gradient. A transport protein is not needed.

Facilitated diffusion across a membrane is movement down a gradient with the aid of a transport protein.

Active transport across a membrane is movement against a gradient with the aid of a transport protein.

© McGraw-Hill Education 29

Phospholipid bilayer barrier

Barrier to hydrophilic molecules and ions due to hydrophobic interior

Rate of diffusion depends on chemistry of solute and its concentration

• High permeability occurs with gases and small uncharged molecules

• Moderate permeability occurs with water and urea

• Low permeability occurs with polar organic molecules

• Very low permeability occurs with ions, charged polar molecules, and large molecules

© McGraw-Hill Education 30

Figure 5.10

© McGraw-Hill Education 31

Cells maintain gradients

Living cells maintain a relatively constant internal environment different from their external environment

Transmembrane gradient • Concentration of a solute is

higher on one side of a membrane than the other

Ion electrochemical gradient • Both an electrical gradient and

chemical gradient

a) Chemical gradient for glucose—a higher glucose concentration outside the cell

b) Electrochemical gradient for Na  —more positive charges outside

the cell and a higher Na  concentration outside the cell

© McGraw-Hill Education 32

Solute concentrations across a membrane

• Isotonic

Equal water and solute concentrations on either side of the membrane

• Hypertonic

Solute concentration is higher (and water concentration lower) on one side of the membrane

• Hypotonic

Solute concentration is lower (and water concentration higher) on one side of the membrane

© McGraw-Hill Education 33

Figure 5.12

a) Outside isotonic

The solute concentration outside the cell is isotonic (or equal) to the inside of the cell.

b) Outside hypertonic

The solute concentration outside the cell is hypertonic to the inside of the cell.

c) Outside hypotonic

The solute concentration outside the cell is hypotonic to the inside of the cell.

© McGraw-Hill Education 34

Osmosis

• Water diffuses through a membrane from an area with more water to an area with less water

• If the solutes cannot move, water movement can make the cell shrink or swell as water leaves or enters the cell

• Osmotic pressure – the tendency for water to move into any cell

© McGraw-Hill Education 35

Osmosis in animal cells

• Animal cells must maintain a balance between extracellular and intracellular solute concentrations to maintain their size and shape

• Crenation – shrinkage of a cell in a hypertonic solution

• Osmotic Lysis – swelling and bursting of a cell in a hypotonic solution

© McGraw-Hill Education 36

Osmosis in plant cells

A cell wall prevents major changes in cell size

Turgor pressure – pushes plasma membrane against cell wall

• Maintains shape and size

Plasmolysis – plants wilting because water leaves plant cells

© McGraw-Hill Education 37

Osmosis in freshwater protists

• Freshwater protists like Paramecium have to survive in a strongly hypotonic environment

• To prevent osmotic lysis, contractile vacuoles take up water and discharge it outside the cell

• Using vacuoles to remove excess water maintains a constant cell volume

(photos): ©Michael Abbey/Science Source

© McGraw-Hill Education 38

Agre Discovered That Osmosis Occurs More Quickly in Cells with Transport Proteins That Allow the Facilitated Diffusion of Water

• Water can passively diffuse across plasma membranes, but some cell types allow water to move across the membrane much faster than predicted

• Peter Agre and colleagues first identified a protein that was abundant in red blood cells, bladder, and kidney cells

• Channel-forming Integral Membrane Protein, 28kDa (CHIP28) • Unlike controls, frog oocytes that expressed CHIP28 swelled

up and lysed when put in a hypotonic medium • CHIP28 was renamed Aquaporin, since it forms a channel that

allows water to pass through the membrane

© McGraw-Hill Education 39

Figure 5.16 Steps 1 through 4 HYPOTHESIS CHIP28 may function as a water channel.

KEY MATERIALS Prior to this work, a protein called CHIP28 was identified that is abundant in red blood cells and kidney cells. The gene that encodes this protein was cloned, which means that many copies of the gene were made in a test tube.

1. Add an enzyme (RNA polymerase) and nucleotides to a test tube that contains many copies of the CHIP28 gene. This results in the synthesis of many copies of CHIP28 mRNA.

2. Inject the CHIP28 mRNA into frog eggs (oocytes). Wait several hours to allow time for the mRNA to be translated into CHIP28 protein at the ER membrane and then moved via vesicles to the plasma membrane.

3. Place oocytes into a hypotonic medium and observe under a light microscope. As a control, also place oocytes that have not been injected with CHIP28 mRNA into a hypotonic medium and observe by microscopy.

4. THE DATA

(4): Courtesy Dr. Peter Agre

© McGraw-Hill Education 40

Figure 5.16 Steps 5 and 6

5. CONCLUSION The CHIP28 protein, now called aquaporin, allows the rapid movement of water across the membrane.

6. SOURCE Preston, G. M., Carroll, T. P., Guggino, W. B., and Agre, P. "Appearance of water channels in Xenopus oocytes expressing red cell CHIP28 protein." Science. 1992.

© McGraw-Hill Education 41

Transport Proteins

• Transport proteins are transmembrane proteins that provide a passageway for the movement of ions and hydrophilic molecules across membranes

• Two classes based on type of movement

Channels

Transporters

© McGraw-Hill Education 42

Channels

• Form an open passageway for the direct diffusion of ions or molecules across the membrane

• Most are gated

• Example: Aquaporins

© McGraw-Hill Education 43

Transporters

• Also known as carriers

• Conformational change transports solute across membrane

• Principal pathway for uptake of organic molecules, such as sugars, amino acids, and nucleotides

© McGraw-Hill Education 44

Transporter types

Uniporter

• Single molecule or ion

Symporter or cotransporter

• Two or more ions or molecules transported in same direction

Antiporter

• Two or more ions or molecules transported in opposite directions

a) Uniporter

b) Symporter

c) Antiporter

© McGraw-Hill Education 45

Active transport

• Movement of a solute across a membrane against its gradient from a region of low concentration to higher concentration

• Energetically unfavorable and requires the input of energy

• Primary active transport uses a pump Directly uses energy to transport solute

• Secondary active transport uses a different gradient Uses a pre-existing gradient to drive transport

© McGraw-Hill Education 46

Figure 5.19

a) Primary active transport b) Secondary active transport

Access the text alternative for slide images.

© McGraw-Hill Education 47

ATP-driven ion pumps generate ion electrochemical gradients

-ATPaseNa K  

Actively transports Na and K  against their gradients

using the energy from ATP hydrolysis

3Na are exported for every

2K  imported into cell

• Antiporter – ions move in opposite directions

• Electrogenic pump – exports one net positive (+) charge

© McGraw-Hill Education 48

Figure 5.20

a) Active transport by the -ATPaseNa K

  b) Mechanism of pumping

1. 3Na bind from cytosol. ATP is hydrolyzed. ADP is released and phosphate (P) is covalently attached to the pump, switching it to the E2 conformation.

2. 3Na  are

released outside of the cell.

3. 2K bind from outside of the cell.

4. Phosphate (Pi) is released, and the pump switches to the E1 conformation.

2K  are released into

cytosol. The process

repeats.

© McGraw-Hill Education 49

Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.

Table 5.3

Table 5.3 Important Functions of Ion Electrochemical Gradients

Function Description

Transport of ions and molecules

Symporters and antiporters use H and Na 

gradients to take up nutrients and export waste products (see Figure 5.19).

Production of energy intermediates

In the mitochondrion and chloroplast, H 

gradients are used to synthesize ATP. Osmotic regulation Animal cells control their internal volume

by regulating ion gradients between the cytosol and extracellular fluid.

Neuronal signaling Na and K gradients are involved in conducting action potentials, the signals transmitted by neurons.

Muscle contraction 2Ca 

gradients regulate the ability of muscle fibers to contract.

Bacterial swimming H gradients drive the rotation of bacterial flagella.

© McGraw-Hill Education 50

Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.

Exocytosis and Endocytosis

Used to transport large molecules such as proteins and polysaccharides

Table 5.4 Examples of Exocytosis and Endocytosis

Exocytosis Description

Hormones Certain hormones, such as insulin, are composed of polypeptides. To exert its effect, insulin is secreted via exocytosis into the bloodstream from beta cells of the pancreas.

Digestive enzymes Digestive enzymes that function in the lumen of the small intestine are secreted via exocytosis from exocrine cells of the pancreas.

Endocytosis Description

Uptake of vital nutrients Many important nutrients are highly insoluble in the blood. Therefore, they are bound to proteins in the blood and then

taken into cells via endocytosis. Examples include the uptake of lipids (bound to low-density lipoprotein) and iron (bound to transferrin protein).

Root nodules Nitrogen-fixing root nodules found in certain species of plants, such as legumes, are formed by the endocytosis of bacteria. After being taken up, the bacterial cells are contained within a membrane-enclosed compartment in the nitrogen-fixing tissue of root nodules.

Immune system Cells of the immune system, known as macrophages, engulf and destroy bacteria via phagocytosis.

© McGraw-Hill Education 51

Exocytosis

Material inside the cell packaged into vesicles and excreted into the extracellular medium

Access the text alternative for slide images.

© McGraw-Hill Education 52

Endocytosis

Endocytosis • Plasma membrane invaginates (folds inward) to

form a vesicle that brings substances into the cell • Three types of endocytosis:

Receptor-mediated endocytosis Pinocytosis Phagocytosis

© McGraw-Hill Education 53

Figure 5.22

Access the text alternative for slide images.

© 2020 McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.

No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.

End of Main Content

Because learning changes everything. ®

www.mheducation.com

Because learning changes everything.®

Chapter 6

Lecture Outline

See separate PowerPoint slides for all

figures and tables pre-inserted into

PowerPoint without notes and animations.

© 2020 McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.

No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.

© McGraw-Hill Education 2

Chapter 6

An Introduction to Energy, Enzymes, and Metabolism

Key Concepts:

• Energy and Chemical Reactions

• Enzymes and Ribozymes

• Overview of Metabolism

• Recycling of Organic Molecules

© McGraw-Hill Education 3

Energy and Chemical Reactions

• Energy = ability to promote change or do work

• Two forms

Kinetic Energy – associated with movement

Potential Energy – due to structure or location

• Chemical energy, the energy in molecular bonds, is a form of potential energy

© McGraw-Hill Education 4

Figure 6.1

a) Kinetic energy b) Potential energy

a: ©moodboard/Corbis; b: ©amanaimages/Corbis

© McGraw-Hill Education 5

Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.

Table 6.1

Table 6.1 Types of Energy That Are Important in Biology

Energy type Description Biological example

Light Light is a form of electromagnetic radiation that is visible to the eye. The energy of light is packaged in photons.

During photosynthesis, light energy is captured by pigments in chloroplasts (described in Chapter 8). Ultimately, this energy is used to produce organic molecules.

Heat Heat is the transfer of kinetic energy from one object to another or from an energy source to an object. In biology, heat is often viewed as kinetic energy that can be transferred due to a difference in temperature between two objects or locations.

Many organisms, including humans, maintain their bodies at a constant temperature. This is achieved, in part, by chemical reactions that generate heat.

Mechanical Mechanical energy is the energy possessed by an object due to its motion or its position relative to other objects.

In animals, mechanical energy is associated with movement due to muscle contraction, such as walking.

Chemical potential Chemical potential energy is potential energy stored in the electrons of molecules. When bonds are broken and rearranged, energy may be released.

The covalent bonds in organic molecules, such as glucose and ATP, store large amounts of energy. When bonds are broken in larger molecules to form smaller molecules, the energy that is released can be used to drive cellular processes.

Electrical/ion gradient The movement of charge or the separation of charges can provide energy. Also, a difference in ion concentration across a membrane constitutes an electrochemical gradient, which is a source of potential energy.

During a stage of cellular respiration called oxidative phosphorylation (described in Chapter 7), an

H  gradient

provides the energy to drive ATP synthesis.

© McGraw-Hill Education 6

Laws of Thermodynamics

First Law of Thermodynamics

“Law of conservation of energy” Energy cannot be created or destroyed, but can be transformed from one type to another

Second Law of Thermodynamics

Transfer of energy from one form to another increases the entropy (degree of disorder) of a system As entropy increases, less energy is available for organisms to use to promote change

© McGraw-Hill Education 7

Figure 6.2 1

© McGraw-Hill Education 8

Figure 6.2 2

© McGraw-Hill Education 9

Change in free energy determines direction of chemical reactions 1

• Total energy = Usable energy + Unusable energy

• Energy transformations involve an increase in entropy (disorder that cannot be harnessed to do work)

• Free energy (G) = amount of energy available to do work

Also called Gibbs free energy

© McGraw-Hill Education 10

Change in free energy determines direction of chemical reactions 2

H = enthalpy or total energy

G = free energy or amount of energy for work

S = entropy or unusable energy

T = absolute temperature in Kelvin (K)

© McGraw-Hill Education 11

Spontaneous reactions 1

• Occur without input of additional energy

• Not necessarily fast, can be slow Breakdown of sucrose to CO2 and H2O is spontaneous, but will take a long time for sugar in a sugar bowl to break down

• Key factor is the free energy change – if ΔG is negative, then process is exergonic and spontaneous

© McGraw-Hill Education 12

Spontaneous reactions 2

• Exergonic = spontaneous

ΔG < 0 (negative free energy change)

Energy is released by reaction

• Endergonic = not spontaneous

ΔG > 0 (positive free energy change)

Requires addition of energy to drive reaction

© McGraw-Hill Education 13

Hydrolysis of ATP

ΔG= −7.3kcal/mole

Reaction favors formation of products

The energy liberated is used to drive a variety of cellular processes

© McGraw-Hill Education 14

Cells use ATP hydrolysis to drive reactions

• An endergonic reaction can be coupled to an exergonic reaction

• The reactions will be spontaneous if the net free energy change for both processes is negative

Collepals.com Plagiarism Free Papers

Are you looking for custom essay writing service or even dissertation writing services? Just request for our write my paper service, and we'll match you with the best essay writer in your subject! With an exceptional team of professional academic experts in a wide range of subjects, we can guarantee you an unrivaled quality of custom-written papers.

Get ZERO PLAGIARISM, HUMAN WRITTEN ESSAYS

Why Hire Collepals.com writers to do your paper?

Quality- We are experienced and have access to ample research materials.

We write plagiarism Free Content

Confidential- We never share or sell your personal information to third parties.

Support-Chat with us today! We are always waiting to answer all your questions.